TROUBLE SHOOTING

Sl.No. Battery Troubles Symptoms / Cause Remedies

1. Over charging a) Excessive gassing

b) Falling active positive plates c) Buckling of plates

d) Increased temperature

a) Reduce the Boost / Float voltage or charing rate reduced to lower value till the specific gravity attains 1.200 b) Add distilled water c) Check the accuracy of voltmeter in the charger if necessary 2 Under charging a) Low specific gravity a) Increase the float

voltage 2.16 to 2.20 volts per cell or increase the charging rate till the specific gravity attains 1.200

b) Check for leakage of electrolyte of current conductors in the charge and battery circuit

c) Reversal of cell voltage

d) Buckling of plates 3 Corrosion of plates Electrolyte impure a) Remove electrolyte

b) Flush with distilled water

c) Refill with pure electrolyte

4 Shedding of active

material a) Over charging of plates b) Charging done at high

rate

c) Material improperly applied on plates

Charging and discharging limits should be maintained at 2.40 volts an 1.85 volts respectively

5 A)Loss of voltage

B) Battery voltage

Sulphation at initial stage can be cured by low rate of repeated charging and discharging. Contact manufacturer / supplier for special treatment

a) Check up connections b) Corroded parts should

be cleaned with warm distilled water and evaporation by too high floating voltage or excessive

a) Replace container immediately in case of leakage

b) Addition of distilled water to maintain the electrolyte level in the leaking cell will result in diminution of

charging capacity and continuous lowering of specific gravity 7 Overflowing in cells

due to increase in electrolyte level even without the addition or distilled

Due to dump atmosphere in the battery room causing

condensation on the cell covers

Improve ventilation in the Battery Room

i) Oil in the diverter switch compartment of all power transformers in service for more than 2 years shall be replaced with filtered and tested oil. Before replacing with fresh oil, flushing of the diverter switch with oil shall be done and the flushed oil sucked out.

Thereafter the oil sample shall be tested once every six months and values recorded. If the results are poor the oil shall be immediately replaced availing shutdown. This is compulsory

ii) A plan of action for thorough inspection of diverter switch for loosening of bolts and connected parts, excessive or uneven burning of the contacts, damage to braided contact leads, carbonization of oil and deposition of carbon on diverter switch, etc, shall be made, on all the diverters of power transformers in service for over 5 years and the defective diverters rectified within a span of 6 months.

33 KV Capacitor Banks – Maintenance and balancing of capacitors in the event of failure at one or more capacitor units guidelines - Issued

In the 33 KV Capacitor banks existing at various substations, the capacitor units are connected in two or three series groups to maintain uniform voltage distribution depending upon the rated voltage of the capacitor units. At present capacitor units are supplied at rated voltage of 7.3 KV or 10.3 KV. Also to obtain the required MVAR, the capacitor units are connected in parallel (numbering 2 to 9) in each series group. Typical examples of Parallel / Series combination of capacitor units in each case are given below in Fig.(1) and Fig(2).

Whether it is single star or double star, the number of series groups / phase depends upon the rated voltage of the capacitor unit viz., 3 series groups if the rated voltage is 7.3 KV and 2 series groups if rated voltage is 10.3 KV.

In the event of failure of one capacitor unit (say in R-phase) it is observed that balancing is done by removing one capacitor each from Y and B-phases as shown in Fig(3)

The above arrangement is not correct, since it results in unequal voltage distribution between the capacitors in series groups.

It can be seen from the figure that against a voltage distribution of V/3 across each series group, the series group containing less capacitors in parallel gets V/2 (i.e.) gets overstressed. Whereas, the other series groups have V/4 (i.e.) are understressed. This result in ultimate failure of the over-stressed capacitors.

It is therefore necessary that number of capacitor units in parallel in each series group in all the three phases on one star bank shall be same.

The correct arrangement of capacitors in the given example is illustrated in Fig(4).

Maintenance schedule for Instrument Transformers – Instructions - Issued

The following routine checks / inspection may be carried out on all Instrument Transformers for increasing the life of the Instrument Transformers and thereby avoiding failures.

a) The oil level of the Instrument Transformers shall be checked periodically. If there is any fall in the oil levels there can be leakage through gaskets or welded joints which should be rectified

b) The surface of the Porcelain insulators should be cleaned periodically. The frequency of cleaning may be altered depending on the pollution level of the Environment.

c) Megger value of primary and secondary winding shall be checked periodically. The minimum values recommended for Instrument Transformers are

a. Primary Winding - 100 Mega Ohms with 1000 V Megger b. Secondary Winding - 20 Mega Ohms with 500 V Megger

d) Whenever there is any doubt regarding the condition of Instrument Transformer, oil samples shall be tested.

The limiting values specified for oil are i) Water content - 40 ppm (max)

ii) Tan delta - 3% (max)

iii) Resistivity - 1 x 20 Ohm Cm. (min)

iv) Acidity - 0.2 (max)

v) Breakdown voltage - 30 KV (min)

e) When oil samples are drawn the hermetic sealing of the Instrument Transformers is broken. To prevent ingress of moisture the Instrument Transformer shall be sealed with dry Nitrogen.

f) The Tangent delta values of primary coil insulation of C.Ts shall be measured if a test tap is provided. The limiting value of Tan delta is 3% (max)

14.5 USEFUL LIVES OF PLANTS

(Extracted from the Electricity (supply) Act, 1948 and as amended upto 1968) Description of asset No. of years of period

A. Land owned under full title Infinity

B. Land held under lease:

a) for investment in the land The period of the lease or the period remaining unexpired on the assignment of the lease.

b) for cost of cleaning site The period of the lease remaining unexpired at the date of clearing the site.

b) Cooling towers and circulating

water system Thirty

c) Hydraulic works forming part of a Hydro-electric system including i) dams, spillways, weirs, canals,

reinforced concrete flumes and syphens.

ii) Reinforced concrete pipelines and surge tanks, steel pipe lines, sluice gates, steel surge tanks, hydraulic control valves and other hydraulic works.

One hundred

Forty

d) Buildings and civil engineering works of a permanent character, not mentioned above:

i) Offices and showrooms

ii) Containing thermoelectric generating plant.

iii) Containing hydro electric generating plant.

iv) Temporary erections such as wooden structures.

v) Roads other than kucha roads.

vi) Others.

e) Transformers, transformer kiosks, substation equipment and other fixed apparatus ( including plant foundations):

i) Transformers (including foundation) having a rating of 100 kilovolt amperes and over.

ii) Others

Thirty five

Twenty five

f) Switchgear, including cable supports operating at nominal voltage higher than 66 KV.

ii) Lines on steel supports operating at nominal voltages, higher than 132 KV but not exceeding 66 KV.

iii) Lines on steel or reinforced concrete supports.

iv) Lines on treated wood supports

Thirty five

l) Static machine tools Twenty

m) Air-conditioning plant:

i) Static

ii) Portable Fifteen

Seven n) i) Office furniture and fittings

ii) Office equipment

iii) Internal wiring including fitting and apparatus. o) apparatus let out on hire

i) Other than motors

ii) Telephone lines and telephones

Fifteen Twenty D. Assets purchased second hand and assets not

otherwise provided for in this table.

Such reasonable period as the state Government determines in each case having regard to the nature, age and condition of the asset at the time of its acquisition by the owner.